Long-term trends in ambient air pollutants and the effect of meteorological parameters in Tabriz, Iran

Abstract

Long-term trends (2006–2017) and spatial variations of four ambient gaseous air pollutants (NO2, NO, SO2, and CO) in Tabriz, Iran were analyzed via the nonparametric Mann-Kendall trend test and Moran's I index. The relationships between ambient air pollutants and meteorological parameters were also investigated using Spearman's rank correlation test. The ambient gaseous air pollutants (NO2, NO, and CO), except for SO2, increased during the study period. The annual mean concentrations of NO2, NO, SO2, and CO were 46.3, 41.8, 29.5 μg/m3, and 3.5 mg/m3, respectively. NO2 concentrations were higher than the WHO AQG (40 μg/m3) and National Air Quality Standard (100 μg/m3) in all years. NO2, NO, SO2, and CO concentrations were higher in winter (51.3, 91.0, 40.7 μg/m3 and 4.0 mg/m3) compared to summer (34.0, 26.0, 21.0 μg/m3 and 3.2 mg/m3), presenting a U-shaped monthly pattern. Based on Spearman's rank correlation analysis, all gaseous air pollutants demonstrated a significant correlation with meteorological parameters (e.g., solar radiation and temperature, wind speed, relative humidity, and precipitation) at the confidence level of 95% (p-value < 0.05). Our findings can help improve the understanding of the air pollutants' spatial and temporal patterns in the studied area in a developing country and present valuable implications for Tabriz policy-makers to tackle air pollution and adopt strategies for air pollution reduction in the future. The findings will also aid pollution controllers and authorities to enact policies to further analyze the costs and benefits of air pollution management programs in Tabriz.